1. Field of the Invention
This invention relates to a durable press process for cellulosic fiber-containing fabrics and more particularly to a process which utilizes formaldehyde and a non-gaseous catalyst to impart wrinkle resistance to cellulosic fiber-containing fabrics.
There have been a great many proposed processes in recent years for treating cellulosic fiber-containing products, such as cloth made of cotton or cotton blends, with formaldehyde to provide durable cross-linking of the cellulose molecules and to thereby impart durable crease resistance and smooth drying characteristics to the goods. However, problems have been encountered, and although a number of the processes have been operated commercially there is a great need for improvement. One problem which recently has taken on critical importance is the quantity of chemicals and amount of energy used to obtain the desired degree of durable press in the fabric. These economic considerations tend to ensure the commercial success of any durable press process which utilizes smaller quantities of chemicals and energy to obtain fabrics having acceptable durable press finishes.
As pointed out in U.S. Pat. No. 3,706,526 granted Dec. 19, 1972, the known processes have tended to lack reproducibility, since control of the formaldehyde cross-linking reaction has been difficult. The process of this patent is said to solve the control problem by controlling moisture present in the cellulosic material during the reaction. The cellulosic material is conditioned to give it a moisture content of between about 4 to 20 percent, preferably 5 to 12 percent, based on the dry weight of the cellulose fiber, and it is then introduced into a gaseous atmosphere containing water vapor, a cellulose cross-linking amount of formaldehyde (e.g. 15 to 60 volume percent) and a catalytic amount of sulfur dioxide. However, the moisture control is difficult and the use of a toxic gas as the catalyst presents a safety factor as well as additional expense for environmental protection by requiring scrubbers and the like to eliminate the toxic substance from any effluent. Also, the presence of the gaseous catalyst and the steam result in corrosion of the curing chamber.
Canadian Pat. No. 897,363, granted Apr. 11, 1972, discloses a process for the formaldehyde cure of cellulosic fibers which comprises applying to the cellulosic material, a solution of zinc chloride, ammonium chloride, phosphoric acid or zinc nitrate, conditioning the fabric to a moisture content of between about 7 & 15 percent based on the dry weight of the fabric, and thereafter exposing the catalyst-containing fabric or article made therefrom to an atmosphere of formaldehyde or formaldehyde vapor (5 to 75 percent volume percent) at a temperature between about 90.degree. and 150.degree.C. The process requires precise moisture control and is said to be limited to the use of the few select catalysts.
It is also known to use methane sulfonic acid as a catalyst in the durable press treatment of cotton using relatively large quantities of a plastic type substance such as dimethylol methyl carbamate (DMMC) as the curing agent. Reinhart et al., "Durable-Press Treatments of Cotton" in Textile Research Journal, Vol. 43, No. 9., September 1973 indicates that methanesulfonic acid was found to function as a strong catalyst for durable-press finishing treatments with its behavior being similar to that of hydroxymethanesulfonic acid, except that it appears to be more stable. However, relatively large quantities 10 to 15 percent of the plastic like or "resin" material DMMC is required. Temperatures of about 250.degree.F to about 320.degree.F are indicated to give about the same results. Because of the large amounts of DMMC and the high temperatures required, this process cannot be considered a viable alternative to a formaldehyde vapor treating process using a low concentration of formaldehyde and low temperature.
Accordingly, a need exists for a simple and economical durable press process which does not depend on precise moisture control to moderate the cross-linking, does not require high concentrations of formaldehyde, high temperatures or utilize a noxious gaseous catalyst or other costly chemicals.